The invention relates to a method of manufacturing a cathode ray tube comprising an electron gun having a number of electrodes with apertures for passing at least one electron beam, in which method during a method step an assembly of electrodes is inspected.
The invention also relates to a device for inspecting an assembly of electrodes.
Cathode ray tubes are used for instance in television apparatuses and computer monitors and oscilloscopes.
Such a method and device are known from European patent application EP 0 793 250. In the known method the position of an upper surface of a first electrode (G1) of an electrode assembly for an electron gun and the position of a lower surface of a second electrode (G2) are measured by means of electric micrometers. The first electrode is the so-called G1-electrode, i.e. the electrode closest to the cathode, when the cathode is installed in the gun. Although such an inspection may be useful, only a very limited inspection, namely of the position of two surfaces is possible. An electron gun may, for various reasons, not fulfil the quality requirements. Inspecting the assembly prior to assembling the electron gun as a whole makes it possible to selectively remove assemblies of electrodes from the manufacturing line, i.e. separate the "good" ones from the "faulty" ones. However, in the known method the risk that, after inspection, an electron gun does not fulfil the requirements is relatively high. The electrical fields which, in operation, form, steer and focus the electron beam(s) are to some extent dependent on the distance between the G1 and G2 electrodes but are also dependent on other parameters.